Vaccines are very cost effective medical interventions. However, although many diseases have been prevented through vaccinations, many others remain to be prevented. Moreover, improved vaccines are needed for a number of diseases for which vaccines already exist. A major hurdle in producing vaccines is the lack of or low immunogenicity of the vaccine. The effectiveness of a vaccine can be enhanced by using adjuvants and delivery systems. Of particular interest are adjuvants that increase the immunogenicity of a vaccine administered by a needle-free method via a mucosal route.